The present invention relates to a filter of the kind comprising a filter chamber into which liquid can flow through a plurality of filter elements and from which liquid can flow continuously. Each filter element is tubular, the first end of the tube being at the filter inlet and the second end being at a cleaning valve. At the first or inlet end there is also a valve which is closed for backwashing. The two valves operate together so that when the inlet valve is open, the cleaning valve is closed and vice versa.
In prior art filters of the kind described the two valves are mounted on a common stem and the stem is moved back and forth by means of an actuator such as a double acting hydraulic cylinder. If upon opening of the cleaning valve there is an obstruction, such as a plant stem at the inlet, and the inlet valve cannot seal fully, the valve system may be distorted and damaged.